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Dujovne 3 Internet-Draft Universidad Diego Portales 4 Intended status: Standards Track M. Richardson 5 Expires: 19 July 2020 Sandelman Software Works 6 16 January 2020 8 IEEE 802.15.4 Information Element encapsulation of 6TiSCH Join and 9 Enrollment Information 10 draft-ietf-6tisch-enrollment-enhanced-beacon-07 12 Abstract 14 In TSCH mode of IEEE STD 802.15.4, opportunities for broadcasts are 15 limited to specific times and specific channels. Nodes in a TSCH 16 network typically frequently send Enhanced Beacon (EB) frames to 17 announce the presence of the network. This document provides a 18 mechanism by which small details critical for new nodes (pledges) and 19 long sleeping nodes may be carried within the Enhanced Beacon. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at https://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on 19 July 2020. 38 Copyright Notice 40 Copyright (c) 2020 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 45 license-info) in effect on the date of publication of this document. 46 Please review these documents carefully, as they describe your rights 47 and restrictions with respect to this document. Code Components 48 extracted from this document must include Simplified BSD License text 49 as described in Section 4.e of the Trust Legal Provisions and are 50 provided without warranty as described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 55 1.1. Use of BCP 14 Terminology . . . . . . . . . . . . . . . . 2 56 1.2. Layer-2 Synchronization . . . . . . . . . . . . . . . . . 2 57 1.3. Layer-3 synchronization: IPv6 Router Solicitations and 58 Advertisements . . . . . . . . . . . . . . . . . . . . . 3 59 2. Protocol Definition . . . . . . . . . . . . . . . . . . . . . 3 60 3. Security Considerations . . . . . . . . . . . . . . . . . . . 5 61 4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 6 62 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 63 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 64 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 65 7.1. Normative References . . . . . . . . . . . . . . . . . . 6 66 7.2. Informative References . . . . . . . . . . . . . . . . . 7 67 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 69 1. Introduction 71 [RFC7554] describes the use of the time-slotted channel hopping 72 (TSCH) mode of [ieee802154]. As further detailed in [RFC8180], an 73 Enhanced Beacon (EB) is transmitted during a slot designated a 74 broadcast slot. 76 1.1. Use of BCP 14 Terminology 78 ::boilerplate bcp14 80 Other terminology can be found in [I-D.ietf-6tisch-architecture] in 81 section 2.1. 83 1.2. Layer-2 Synchronization 85 As explained in section 6 of [RFC8180], the Enhanced Beacon (EB) has 86 a number of purposes: synchronization of ASN and Join Metric, 87 carrying timeslot template identifier, carrying the channel hopping 88 sequence identifier, and indicating the TSCH SlotFrame. 90 The EB is used by nodes already part of a TSCH network to annouce its 91 existence. Receiving an EB allows a Joining Node (pledge) to learn 92 about the network and synchronize to it. The EB may also be used as 93 a means for a node already part of the network to re-synchronize 94 [RFC7554]. 96 There is a limited number of timeslots designated as a broadcast slot 97 by each router in the network. Considering 10ms slots and a slot- 98 frame length of 100, these slots are rare and could result in only 1 99 slot/s for a broadcast, which needs to be used for the beacon. 100 Additional broadcasts for Router Advertisements, or Neighbor 101 Discovery could even more scarce. 103 1.3. Layer-3 synchronization: IPv6 Router Solicitations and 104 Advertisements 106 At layer 3, [RFC4861] defines a mechanism by which nodes learn about 107 routers by receiving multicast Router Advertisements (RA). If no RA 108 is heard within a set time, then a Router Solicitation (RS) may be 109 sent as multicast, to which an RA will be received, usually unicast. 111 Although [RFC6775] reduces the amount of multicast necessary to do 112 address resolution via Neighbor Solicitation (NS) messages, it still 113 requires multicast of either RAs or RS. This is an expensive 114 operation for two reasons: First, there are few multicast timeslots 115 for unsolicited RAs; and second, if a pledge node does not hear an 116 RA, and decides to send a RS, a broadcast aloha slot is consumed with 117 unencrypted traffic. In this case, a unicast RS may be sent in 118 response. 120 This is a particularly acute issue for the join process for the 121 following reasons: 123 1. use of a multicast slot by even a non-malicious unauthenticated 124 node for a Router Solicitation (RS) may overwhelm that time slot. 126 2. it may require many seconds of on-time before a new pledge hears 127 a Router Advertisement (RA) that it can use. 129 3. a new pledge may listen to many Enhanced Beacons (EB) before it 130 can pick an appropriate network and/or closest Join Assistant to 131 attach to. If it must listen for a RA as well as find the 132 Enhanced Beacon (EB), then the process may take a very long time. 134 This document defines a new IETF IE subtype to provide join and 135 enrollment information to prospective pledges in a more efficient 136 way. 138 2. Protocol Definition 140 [RFC8137] creates a registry for new IETF IE subtypes. This document 141 allocates a new subtype. 143 The new IE subtype structure is as follows. As explained in 144 [RFC8137] the length of the Sub-Type Content can be calculated from 145 the container, so no length information is necessary. 147 1 2 3 148 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 149 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 150 | TBD-XXX |R|P| res | proxy prio | rank priority | 151 +-+-+-+-+-+-+-+-+-+-------------+-------------+-----------------+ 152 | pan priority | | 153 +---------------+ + 154 | Join Proxy lower-64 | 155 + (present if P=1) + 156 | | 157 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 158 | | | 159 +-+-+-+-+-+-+-+-+ + 160 | network ID | 161 + variable length, up to 16 bytes + 162 ~ ~ 163 + + 164 | | 165 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 166 | | 167 +-+-+-+-+-+-+-+-+ 169 Figure 1: IE subtype structure 171 R the Router Advertisement R-flag is set if the sending node will 172 act as a Router for host-only nodes that need addressing via 173 unicast Router Solicitation messages. 175 P if the Proxy Address P-flag is set, then the lower 64-bits of the 176 Join Proxy's link-local address follows the network ID. If the 177 Proxy Address bit is not set, then the Link Layer address of the 178 Join Proxy is identical to the Layer-2 8-byte address used to 179 originate this enhanced beacon. In either case, the destination 180 layer-2 address of this beacon may use the layer-2 address which 181 was used to originate the beacon. 183 proxy priority (proxy prio) this field indicates the willingness of 184 the sender to act as join proxy. Lower value indicates greater 185 willingness to act as a Join Proxy as described in 186 [I-D.ietf-6tisch-minimal-security]. Values range 0x00 (most 187 willing) to 0x7e (least willing). A priority of 0x7f indicates 188 that the announcer should never be considered as a viable 189 enrollment proxy. Only unenrolled pledges look at this value. 191 rank priority the rank "priority" is set by the 6LR which sent the 192 beacon and is an indication of how willing this 6LR is to serve as 193 an RPL parent within a particular network ID. This is a local 194 value to be determined in other work. It might be calculated from 195 RPL rank, and it may include some modifications based upon current 196 number of children, or number of neighbor cache entries available. 197 This value MUST be ignored by pledges, it is for enrolled devices 198 only. 200 pan priority the pan priority is a value set by the DODAG root to 201 indicate the relative priority of this LLN compared to those with 202 different PANIDs. This value may be used as part of the 203 enrollment priority, but typically is used by devices which have 204 already enrolled, and need to determine which PAN to pick. 205 Unenrolled pledges MAY consider this value when selecting a PAN to 206 join. Enrolled devices MAY consider this value when looking for 207 an eligible parent device. 209 Join Proxy lower-64 if the P bit is set, then 64 bits (8 bytes) of 210 address are present. This field provides the suffix of the Link- 211 Local address of the Join Proxy. The associated prefix is well- 212 known as fe80::/64. 214 network ID this is a variable length field, up to 16-bytes in size 215 that uniquely identifies this network, potentially among many 216 networks that are operating in the same frequencies in overlapping 217 physical space. The length of this field can be calculated as 218 being whatever is left in the Information Element. 220 In a 6tisch network, where RPL [RFC6550] is used as the mesh routing 221 protocol, the network ID can be constructed from a SHA256 hash of the 222 prefix (/64) of the network. That is just a suggestion for a default 223 value. In some LLNs where multiple PANIDs may lead to the same 224 management device (the JRC), then a common value that is the same 225 across all PANs MUST be configured. 227 3. Security Considerations 229 All of the contents of this Information Element are sent in the 230 clear. The containing Enhanced Beacon is not encrypted. 232 The Enhanced Beagon is authenticated at the layer-2 level using 233 802.15.4 mechanisms using the network-wide keying material. Nodes 234 which are enrolled will have the network-wide keying material and can 235 validate the beacon. 237 Pledges which have not yet enrolled are unable to authenticate the 238 beacons. 240 4. Privacy Considerations 242 The use of a network ID may reveal information about the network. 243 The use of a SHA256 hash of the DODAGID, rather than using the 244 DODAGID directly provides some cover the addresses used within the 245 network. The DODAGID is usually the IPv6 address of the root of the 246 RPL mesh. 248 An interloper with a radio sniffer would be able to use the network 249 ID to map out the extent of the mesh network. 251 5. IANA Considerations 253 Allocate a new number TBD-XXX from Registry IETF IE Sub-type ID, as 254 defined by [RFC8137]. This entry should be called 6tisch-Join-Info, 255 and should refer to this document. 257 6. Acknowledgements 259 Thomas Watteyne provided extensive editorial comments on the 260 document. Carles Gomez Montenegro generated a detailed review of the 261 document at WGLC. Tim Evens provided a number of useful editorial 262 suggestions. 264 7. References 266 7.1. Normative References 268 [BCP14] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 269 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 270 May 2017, . 272 [I-D.ietf-6tisch-minimal-security] 273 Vucinic, M., Simon, J., Pister, K., and M. Richardson, 274 "Constrained Join Protocol (CoJP) for 6TiSCH", Work in 275 Progress, Internet-Draft, draft-ietf-6tisch-minimal- 276 security-15, 10 December 2019, . 280 [ieee802154] 281 IEEE standard for Information Technology, ., "IEEE Std. 282 802.15.4, Part. 15.4: Wireless Medium Access Control (MAC) 283 and Physical Layer (PHY) Specifications for Low-Rate 284 Wireless Personal Area Networks", 2015, 285 . 288 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 289 Requirement Levels", BCP 14, RFC 2119, 290 DOI 10.17487/RFC2119, March 1997, 291 . 293 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 294 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 295 DOI 10.17487/RFC4861, September 2007, 296 . 298 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 299 Bormann, "Neighbor Discovery Optimization for IPv6 over 300 Low-Power Wireless Personal Area Networks (6LoWPANs)", 301 RFC 6775, DOI 10.17487/RFC6775, November 2012, 302 . 304 [RFC8137] Kivinen, T. and P. Kinney, "IEEE 802.15.4 Information 305 Element for the IETF", RFC 8137, DOI 10.17487/RFC8137, May 306 2017, . 308 7.2. Informative References 310 [I-D.ietf-6tisch-architecture] 311 Thubert, P., "An Architecture for IPv6 over the TSCH mode 312 of IEEE 802.15.4", Work in Progress, Internet-Draft, 313 draft-ietf-6tisch-architecture-28, 29 October 2019, 314 . 317 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 318 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 319 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 320 Low-Power and Lossy Networks", RFC 6550, 321 DOI 10.17487/RFC6550, March 2012, 322 . 324 [RFC7554] Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using 325 IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the 326 Internet of Things (IoT): Problem Statement", RFC 7554, 327 DOI 10.17487/RFC7554, May 2015, 328 . 330 [RFC8180] Vilajosana, X., Ed., Pister, K., and T. Watteyne, "Minimal 331 IPv6 over the TSCH Mode of IEEE 802.15.4e (6TiSCH) 332 Configuration", BCP 210, RFC 8180, DOI 10.17487/RFC8180, 333 May 2017, . 335 Authors' Addresses 337 Diego Dujovne (editor) 338 Universidad Diego Portales 339 Escuela de Informatica y Telecomunicaciones, Av. Ejercito 441 340 Santiago, Region Metropolitana 341 Chile 343 Phone: +56 (2) 676-8121 344 Email: diego.dujovne@mail.udp.cl 346 Michael Richardson 347 Sandelman Software Works 349 Email: mcr+ietf@sandelman.ca